1. Field of the Invention
The invention relates to a device for scraping off materials deposited and/or preventing them from being deposited on the internal surface of an elongated tube having a relatively small diameter.
2. Description of the Prior Art
It frequently occurs that a portion of fluid is deposited on internal wall surfaces of tubes and disturbs the operation of a process, wherein tubes are used for reaction, crystallization, evaporation, absorption, cooling, heating or fluid transport. For instance, a process is carried out, wherein continuous polymerization of methacrylic acid ester is conducted in a stirred tank reactor, the resulting polymerization product taken out from the reactor being sent to a multi-tubular head exchanger and cooled therein to remove a portion of the heat of reaction, the fluid being returned into the reactor thereafter, whereby the polymer is deposited on the internal walls of the reactor and the heat exchanger tubes after a long operation. This deposit results in the reduced thermal conductivity of the internal walls which causes an uncontrollably rapid reaction, consequently rendering the process impossible to continuously operate for a long duration.
To solve such a problem, there is proposed a method using a scraper type polymerization tank reactor disclosed by, for an example, Japanese Patent Publication No. 2645/1965. This method comprises a stirred tank polymerization reactor provided with a screw type agitator in a draft tube, with scraper blades being fixed on the edge of the screw of the screw type agitator and adapted to be pressed against the internal wall of the draft tube to scrape off material therefrom. The screw type agitator is also provided with a horizontal arm on the screw drive shaft thereof, with scraper blades attached on said arm to scrape off deposits from the internal wall of the jacket and the external wall of the draft tube, and thus the polymerization is conducted while those surfaces are being scraped. However, this method requires structures such as rotating blades inside a device, and therefore, is not suitable for a reactor having a small internal diameter, especially to a multi-tubular heat exchanger for scraping the internal walls of its tubes.